This invention relates to ducts for housing cable and, in particular, to ducts for housing communication cable.
In the placing of conventional copper telephone cable, the cable is run through a duct which is used to house and protect the cable. Prior to placing the cable in the duct a cone shaped element is passed through the duct to clear away any debris and ensure a clear passage for the cable. Also attached to the cone is an end of a cable pull-line. Once the cone and attached end of the pull-line are through the duct, the other end of the line is affixed to a telephone cable and the cable pulled through the duct.
In order to pass the cone through the duct, a pressure differential is created in the duct. This requires that the individual components of the duct and their interconnections provide an air-tight passage. Otherwise, air leaks will occur and insufficient pressure will be developed to pull the cone through the line.
As the telephone industry has turned to the use of fiber optic cable for telephone transmission, it has had to develop techniques for placing the smaller diameter fiber optic cable. These techniques have continued to utilize the pressurized cone procedure for pulling cable through the ducts, since this procedure results in minimizing installation time.
At present, placing of fiber optic cable is accomplished by first pulling three one inch inner ducts through the usual four inch copper cable duct. The pressurized cone procedure is then used to pull a fiber optic cable through a first duct and to pull a small copper cable through a second duct. The copper cable is needed to provide talking channels between various installation points. The third inner duct serves as a spare, since it cannot be used without an associated cable for talking channels.
In many cases, the pulling of the three one inch ducts through the four inch duct is extremely difficult and in certain cases not possible to accomplish. This is particularly true where the four inch duct has vertical and horizontal bends. These bends may be created when placing the duct and may be a result of cable congestion and/or location.
In order to provide for an additional fiber optic cable in a conventional four inch duct and to avoid the material and labor costs of providing and pulling three inner ducts, it has now been proposed that the four inch duct itself be modified by segmenting the duct into four one inch compartments, two of which for receiving fiber optic cable and the other two of which for receiving associated talking channel copper cable. While such a segmented duct would increase the cable capacity by one and would not require separate inner ducts, the duct must also be designed so that pulling of each cable through its associated compartment can be achieved utilizing the aforementioned pressurized cone procedure. This requires that the individual compartments be air-tight and that the duct be connectible to like ducts in a manner to preserve this condition.
It would also be desirable if such a segmented duct could be further designed so that connection to similar ducts automatically aligns corresponding compartments. Finally, it would be advantageous if the duct could be made in long lengths, while still being capable of being cut to shorter lengths which when joined to similar ducts preserves the alignment as well as air-tightness of the corresponding compartments.
It is therefore an object of the present invention to provide a cable duct having one or more of the above-mentioned features.
It is a further object of the present invention to provide a segmented duct for fiber optic cable wherein the duct can be joined to similar ducts, while maintaining an air-tight condition for the individual compartments of the ducts.
It is yet a further object of the present invention to provide a duct of the last mentioned type which can be of long length and which can be cut into shorter lengths which can then be joined to similar ducts so as to maintain alignment of corresponding compartments and an air-tight condition.